Many organisms are able to regenerate whole limbs and portions of tissues and organs after amputation or significant damage. However, the molecular mechanisms that ensure maintenance of cell fate and proper re- patterning of the regenerating structure are unknown. The long-term goal is to understand how damaged tissue regenerates a functional body part. The overall objective of this proposal is to identify the developmental and novel patterning processes that are critical for proper formation of the regenerated Drosophila imaginal wing, an ideal model system because of the simplicity of the tissue, as well as its genetic tractability, well- characterized development, and wealth of available experimental tools. The central hypothesis is that regeneration resembles development in some ways, but also employs alternate mechanisms to maintain or establish patterning and cell fate. This hypothesis was formulated based on preliminary data generated in laboratory of the applicant; including mutations identified in a genetic screen that specifically affect patterning during regeneration, not development. The rationale for the proposed research is that identification of patterning mechanisms required during regeneration has the potential to guide efforts to enable and manipulate regeneration in human tissues that normally do not regrow after damage. This proposed work will be accomplished through the following specific aims: 1) Characterize patterning during regeneration with high spatial and temporal resolution; 2) Determine the regeneration-specific mechanism through which taranis maintains posterior cell identity; and 3) Identify additional regeneration-specific patterning mechanisms. Under the first aim, repatterning during regeneration will be mapped in fine detail by following changes in expression of known patterning genes and carrying out transcriptional profiling of the regeneration blastema. Under the second aim, the mechanism through which taranis ensures maintenance of engrailed expression and posterior cell fate during regeneration will be determined, using feasible genetic and biochemical approaches. Under the third aim, new genes and mechanisms that regulate cell fate and patterning during regeneration will be identified using two complementary approaches: 1) continuation of the already successful genetic screen and characterization of patterning mutants, and 2) characterization of regeneration genes identified through transcriptional profiling of purified blastema cells. This approach is innovative because it uses the full power of Drosophila genetics as well as novel cellular techniques to identify genes important for cell fate and patterning during regeneration. This re- search will be significant because it will identify novel, regeneration-specific molecular mechanisms that ensure regrowth of a functional structure after extensive tissue loss. Ultimately this improved understanding of regeneration has the potential to enable regrowth of damaged tissues, organs and appendages that do not normally regenerate.